Question : In the given figure, PQR is a quadrant whose radius is 7 cm. A circle is inscribed in the quadrant as shown in the figure. What is the area (in cm2) of the circle?
Option 1: $385-221\sqrt{2}$
Option 2: $308-154\sqrt{2}$
Option 3: $154-77\sqrt{2}$
Option 4: $462-308\sqrt{2}$
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Correct Answer: $462-308\sqrt{2}$
Solution :
Let the radius of the circle = $r$ cm The radius of the quadrant = QM = QR = QP = 7 cm From the figure, $OS=OT=OM=QT=r$ cm ⇒ $OQ=(7-r)$ cm In $\triangle QTO$, $OQ^2=OT^2+QT^2$ ⇒ $(7-r)^2=r^2+r^2$ ⇒ $(7-r)^2=2r^2$ ⇒ $7-r=r\sqrt2$ ⇒ $r=\frac{7}{\sqrt2+1}=7(\sqrt2-1)$ The area of the circle = $\pi r^2$ ⇒ The area of the circle = $\pi [7(\sqrt2-1)]^2$ ⇒ The area of the circle = $\frac{22}{7} [7(\sqrt2-1)]^2$ ⇒ The area of the circle = $22×7×(3-2\sqrt2)=462-308\sqrt{2}$ cm 2 Hence, the correct answer is $462-308\sqrt{2}$.
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